Battery packs suitable for use with battery powered appliances

ABSTRACT

Cooling air intake port ( 52 ), cooling air exhaust port ( 55 ), and securing walls ( 86, 87 ), which contact and secure the side surfaces of one or more battery cells ( 72 ), may be defined within two battery pack housing halves ( 50, 80 ). When battery pack ( 99 ) is assembled, at least one cooling air passage ( 91, 92 ) is defined by the side surfaces of the battery cells, the interior surface of the battery pack housing, and the securing walls. The cooling air passage connects the cooling air intake port to the cooling air exhaust port. Further, the securing walls isolate or physically separate the cooling air passage from battery terminals ( 72   a   , 72   b ). By forcing cooling air through the cooling air passage, the battery cells can be effectively and efficiently cooled. In addition, if the battery terminals are isolated from the cooling air by the securing walls, the electrical contact areas of the battery cells are protected or shielded against outside moisture and foreign substances that may be introduced into the battery pack by the cooling air.

CROSS-REFERENCE

This application is a continuation of U.S. patent application Ser. No.11/733,644 filed on Apr. 10, 2007, which is a continuation of patentapplication Ser. No. 10/281,742, filed Oct. 20, 2002, now U.S. Pat. No.7,238,443 issued Jul. 3, 2007, which claims the benefit of U.S.provisional application Ser. No. 60/332,985, filed Nov. 5, 2001.

This application also claims priority based on Japanese patentapplication serial number 2001-337045, filed Nov. 1, 2001, the entirecontents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to rechargeable battery packs having oneor more battery cells disposed within a case or housing. This batterypack may be electrically coupled to a battery charger in order to chargethe battery cells. Thereafter, the charged battery pack may be connectedto a power tool or another battery-powered appliance in order to supplycurrent to the tool or device.

2. Description of the Related Art

Generally speaking, known rechargeable battery packs are installed in abattery charger in order to re-charge the batteries. A plurality ofindividual batteries or battery cells may be connected in paralleland/or in series in order to provide the desired battery voltage andoutput current. During recharging, the battery cells typically generateheat, thereby increasing the temperature of the battery cells. Variousarrangements for cooling the battery cells during the rechargingoperation have been proposed.

Nickel metal hydride batteries provide increased or greater batterycapacity (energy density) as compared to other known batterytechnologies, such as nickel-cadmium batteries, thereby making nickelmetal hydride batteries particularly suitable for driving power tools.In addition, nickel metal hydride batteries do not include cadmium,thereby providing a more environmentally friendly power storage device.However, thus far, the use of nickel metal hydride batteries has beenlimited in the power tool field, because nickel metal hydride batteriesare known for generating a relatively large amount of heat when knowncharging techniques are utilized to re-charge the batteries, especiallyif a relatively quick charge is performed. If the temperature of thenickel metal hydride battery cells is allowed to become higher than acertain threshold temperature (typically, between about 50°-60° C. forcurrent nickel metal hydride battery technologies), the life of thebattery cell may be significantly shortened due to internal damagecaused by the relatively high temperature. The nickel metal hydridebatteries, of course, also could be charged relatively slowly in orderto minimize the likelihood of excessive temperature increases. However,slow charging will naturally reduce the desirability of utilizing nickelmetal hydride batteries, because the power tool operator must wait acomparatively longer time to recharge the battery pack for further use.

Thus, there is a long-felt need in the power tool field, as well asother fields that utilize rechargeable batteries, to develop batterypack designs and battery charging technologies that will enable nickelmetal hydride batteries, or other battery types that become hot duringrecharging, to be quickly charged without overheating and thus damagingthe battery cells.

Furthermore, battery-driven power tools generally must be operated usingrelatively large currents in order to operate with the same efficiencyand effectiveness as power tools driven by a commercial AC power source.Thus, if a short circuit develops within the battery pack, seriousproblems could result due to the relatively high currents that can besupplied by nickel metal hydride batteries. Therefore, the battery cellsare preferably isolated or shielded from outside moisture and foreignsubstances in order to prevent or reduce the possibility of shortcircuits within the battery pack. Moreover, it is preferable touniformly cool the battery cells during the recharging operation so thatall the battery cells are maintained at substantially the sametemperature. In this case, it is possible to avoid the possibility thatone or more battery cells will reach a temperature that will causepermanent damage to the battery cell, and thereby make the battery packinoperative for its intended purpose.

European Patent Publication No. 0 940 864 describes a battery packstructure for nickel metal hydride battery cells. However, this knowndesign focuses primarily on cooling the battery cells and does not teachany techniques for protecting the battery cells from moisture andforeign substances. In fact, the battery cells of European PatentPublication No. 0 940 864 are cooled by directly contacting the batterycells with forced air supplied from the battery charger and/or the powertool. Thus, moisture or foreign substances can easily contact thebattery terminals and cause degradation, which may lead to shortcircuits. Further, the battery packs of European Patent Publication No.0 940 864 rely upon metal heat sinks in order to uniformly cool thebattery cells within the battery pack. However, a metal heat sink willnaturally increase the overall weight of the battery pack, as well asthe cost of manufacturing the battery packs.

In European Patent Publication No. 0 994 523, the present Applicantproposed a battery pack design in which a plurality of battery cells isdisposed within a dual-wall housing. An inner case optionally may beformed, either entirely or partially, from a thermally conductivematerial, such as aluminum. Further, the inner case may directly contactthe battery cells in order to uniformly cool the battery cells. Inaddition, the inner case may substantially surround or enclose thebattery cells in order to protect the battery cells from outsidemoisture and foreign substances. Moreover, the inner case may be housedor disposed within an outer case and a cooling-air passage may bedefined between the inner and outer cases. Thus, the battery pack designof European Patent Publication No. 0 994 523 enables uniform cooling ofthe battery cells while preventing moisture and foreign substances fromcontacting the battery terminals. Further, the double housing serves toprotect the power tool operator in the event that a short circuithappens to develop between the battery cells.

Thus, European Patent Publication No. 0 994 523 provides a commerciallyuseful battery pack design, which effectively cools nickel metal hydridebatteries during the recharging operation and effectively preventsdegradation that could lead to dangerous short circuits.

SUMMARY OF THE INVENTION

Although European Patent Publication No. 0 994 523 provides severaladvantages over the known art, it is one object of the present teachingsto provide further improvements in battery pack designs. For example, inone aspect of the present teachings, the metal heat sink can be removedor eliminated without sacrificing cooling efficiency. Thus, lower weightand less expensive battery packs can be made using the presentteachings. Such battery pack designs are particularly useful with nickelmetal hydride batteries, although the present battery pack designs, ofcourse, can be utilized with any type of rechargeable battery and morepreferably, with rechargeable batteries that generate heat duringrecharging and/or during use (discharging).

In another aspect of the present teachings, battery pack designs aretaught that are particularly useful with battery cells, such as nickelmetal hydride batteries, that require strict temperature control duringcharging and isolation from external moisture and foreign substances inorder to prevent short circuits and degradation of the battery cells.

In one embodiment of the present teachings, a plurality of elongatedbattery cells (e.g., nickel metal hydride battery cells) may bepositioned in a side-by-side relationship such that the respective endfaces (i.e., the battery terminals) are positioned within the sameplane, or substantially the same plane. In this embodiment, the endfaces or terminals of the respective battery cells are preferablyisolated from a cooling air passage in order to prevent degradation ofthe battery terminals, as well the contacts (conductive material) thatextend between the battery terminals. The battery packs also maygenerally include a cooling air intake port, a cooling air exhaust port,and supports or securing walls for receiving and securing the batterycells within the battery pack. The cooling air passage preferablyextends within the battery pack between the cooling air intake port andthe cooling air exhaust port. Further, the cooling air passage may bepartially defined by the side surfaces of the respective battery cellsand the interior surface of the battery pack housing. The supports maybe utilized to isolate the cooling air passage from the end faces orterminals of the battery cells.

In such an embodiment, the cooling air may be effectively andefficiently utilized to cool the battery cells, because the cooling airwill directly contact the respective side surfaces of the battery cells.However, because the end faces or terminals of the battery cells areisolated or physically separated from the cooling air passage, theelectrical contacts extending between the battery cells group areeffectively protected from outside moisture and foreign substances.Thus, degradation of the battery contacts can be minimized while stilleffectively cooling the battery cells during a charging operation.

In another embodiment of the present teachings, a plurality of elongatedbattery cells may be disposed in a side-by-side relationship such thatthe side surfaces of the battery cells are disposed closely together(e.g., adjacent to each other). Optionally, the respective side surfacesmay contact each other. In these embodiments, the supports (or securingwalls) may secure the battery cells by contacting and supporting theoutermost peripheral surface of the battery cells. The supports may bedefined or disposed within the interior of the battery pack housing(case). In addition, the cooling air passage may be partially defined bythe outermost peripheral surface of the battery cells, the interiorsurface of the battery pack housing, and/or the support(s). In thiscase, the supports may at least partially isolate or physically separatethe cooling air passage(s) from the end faces (terminals) of the batterycells. Optionally, a temperature sensor may be disposed within theisolated space (e.g., the space containing the end faces or terminals ofthe battery cells that is isolated from the cooling air passage). Thetemperature sensor may output signals representing the batterytemperature and such battery temperature signals may be communicated tothe battery charger (e.g., to a CPU disposed within the battery charger)in order to control, adjust and/or terminate the recharging operation.

In these embodiments as well, the cooling air forced into the batterypack can effectively cool the battery cells, because the cooling air maydirectly contact the outermost peripheral surface of the battery cells.Further, because the end faces or terminals of the battery cells areisolated from the cooling air, the electrical contact areas of thebattery cells are protected from outside moisture and foreignsubstances. Moreover, the temperature sensor also may be isolated fromthe cooling air. Therefore, the temperature sensor will measure thetemperature of the battery cells more accurately than if the cooling airdirectly contacts the temperature sensor. Furthermore, if the batterycells are disposed such that the peripheral side surfaces of the batterycells closely contact each other, heat can be readily conducted fromhigher-temperature battery cells to lower-temperature battery cells. Asa result, the temperatures of the plurality of battery cells may besubstantially unified, e.g., during a charging operation, therebypreventing degradation of the battery cells caused by overheating.

Optionally, the cooling air passage may preferably extend transverselyto the longitudinal direction of the elongated battery cells. In thiscase, the design of the cooling air passage can be easily modifiedaccording to changes in the number of battery cells that will bedisposed within the battery pack. As a result, the temperatures of therespective battery cells can be uniformly maintained without requiringsignificant battery pack design changes. On the other hand, if thecooling air passage extends in parallel with the longitudinal directionof the elongated battery cells, it may be difficult to properly adjustthe air volume distribution in branched cooling air passages.

In another embodiment of the present teachings, an insulating materialmay be disposed on the peripheral side surfaces of the battery cellsthat are closest to the cooling air intake port (i.e., upstream batterycells). Generally speaking, the cooling air forced into the battery packwill be the lowest temperature (coolest) at the cooling intake port andthe highest temperature (hottest) at the cooling air exhaust port,because the cooling air will absorb heat from the battery cells as thecooling air passes through the cooling air passage. Therefore, thebattery cells disposed nearest to the cooling air intake port along thecooling air passage (i.e., the upstream portion of the cooling airpassage) will be cooled by relatively cooler air, whereas the batterycells disposed farthest from the cooling air intake port along thecooling air passage (i.e., the downstream portion of the cooling airpassage) will be cooled by relatively warmer air. Consequently, theupstream battery cells may be cooled more effectively than thedownstream battery cells. In the absence of modifications to overcomethis phenomenon, the respective battery cells may not be cooled to auniform temperature and thus, some downstream battery cells may besubject to degradation caused by overheating.

In European Patent Publication No. 0 940 864, a metal heat sink contactsthe battery cells that are expected to be the most difficult to cool(i.e., the downstream battery cells). However, a metal heat sinkincreases the overall weight of the battery pack as well asmanufacturing costs. On the other hand, many insulating materials, suchas plastic materials are both lightweight and inexpensive.

Thus, in another embodiment capable of uniformly cooling the batterycells within the battery pack, a relatively lightweight and low-costinsulting material may be disposed on or proximal to the upstreambattery cells. In this case, the upstream battery cells will be cooledless efficiently than if no insulating material is provided. That is, ifinsulating material is disposed on (or proximal to) one or more of theupstream battery cells, the cooling air will absorb less heat and thus,the cooling air that contacts the downstream battery cells will becooler or lower temperature than if no insulating material is provided.By contacting (cooling) the downstream battery cells with lowertemperature cooling air, the downstream battery cells can be cooled moreeffectively. Thus, by utilizing the present teachings, all the batterycells easily can be uniformly maintained at the same, or substantiallythe same, temperature during the recharging operation. Moreover, becauserelatively low cost (and lightweight) insulating materials may beutilized in order to maintain all the battery cells at a uniformtemperature, instead of a relatively high cost (and heavy) metallic heatsink, battery packs according to the present teachings can bemanufactured at a lower cost (and lesser weight) than known battery packdesigns.

Thus, rather than disposing a relatively heavy, metal heat sink materialon the batteries that are least efficiently cooled (i.e., the downstreambatteries), a lightweight, heat insulating material is preferablydisposed on the battery cells that typically are most efficiently cooled(i.e., the upstream batteries). However, a combination of insulatingmaterial and heat sink material optionally may be utilized within thepresent battery packs. For example, insulating material may be disposedon the upstream batteries and heat sink material (e.g., metal heat sinkmaterial) may be disposed on the downstream batteries. In this case, theupstream and downstream batteries can be uniformly cooled and the totalamount of heat sink material can be reduced as compared to knowndesigns.

In these embodiments, the battery cells that are closest to the coolingair intake port along the cooling air passage, which battery cells maybe more readily cooled by the cooling air, are not overcooled becausethese battery cells are partially or entirely covered with insulatingmaterial, such as heat insulating sheets. Herein, the term “insulatingmaterial” is intended to encompass any material(s) that possess(es) theproperty of reducing the ability of the cooling air to remove heat fromthe side surfaces of battery cells. Representative insulating materialsinclude, e.g., resin sheets and resin covers, because these insulatingmaterials are relatively durable and inexpensive. However, otherinsulating materials, including paper, also may be effectively utilizedwith the present teachings.

In one representative embodiment, the insulating material may be asubstantially rigid resin cover that defines an air gap or clearancebetween the resin cover and the peripheral side surfaces of the batterycells. In this representative embodiment, air trapped within the air gapbetween the resin cover and the battery cells may also serve as aninsulating material. Thus, such a design may further reduce the weightand cost of the battery pack without reducing the cooling efficiency ofthe design by effectively utilizing an air layer or air pocket as aninsulating material.

In another embodiment of the present teachings, one or more cooling airdirectors may be disposed along the cooling air path in order to directcooling air toward the side surface(s) of one or more of the batterycells. As noted above, the battery cells nearest to the cooling airexhaust port (i.e., the downstream batteries) along the cooling airpassage are generally cooled less efficiently than the upstream batterycells, because the cooling air is heated by the upstream batteriesbefore reaching the downstream batteries. In order to increase thecooling efficiency of the relatively warmer cooling air, the cooling airpassage may include, e.g., one or more cooling air directors thatspecifically direct the cooling air towards the battery cell(s) that is(are) generally the least efficiently cooled by the cooling air. Bycausing a portion of the cooling air to directly impact the side surfaceof such difficult-to-cool battery cell(s), the cooling air passage andthe cooling air can more effectively cool all the battery cells in auniform manner. Various techniques for designing such air directors aretaught below in more detail.

In another embodiment of the present teachings, the cross-sectional areaof the cooling air passage may generally increase along the cooling airpassage (e.g., from the cooling air intake port to the cooling airexhaust port). For example, the upstream portion of the cooling airpassage (i.e., the portion of the cooling air passage nearest to thecooling air intake port) may have a relatively small cross-section andthe upstream portion of the cooling air passage may contact a relativelysmall area of the peripheral side surfaces of the upstream batterycells. That is, the upstream portion of the cooling air passage maydirectly communicate with only a relatively small portion of theperipheral side surfaces of the battery cells. However, near the coolingair exhaust port, the downstream portion of the cooling air passage mayhave a relatively large cross section and may contact a relatively largearea of the peripheral side surfaces of the downstream battery cells.

In this representative embodiment, the cooling air that is nearest tothe cooling air exhaust port has already been heated by the upstreambattery cells and thus has less capacity to cool the downstream batterycells. However, by increasing the respective areas of the downstreambattery cells that are directly exposed to (communicate with) thecooling air passage, the downstream battery cells can be moreeffectively cooled by the warmer cooling air. For example, if thecross-sectional area of the cooling air passage increases towards thedownstream portion of cooling air passage, the cooling air will movemore slowly in the downstream portion of the cooling air passage than inthe upstream portion of the cooling air passage. Consequently, thecooling air moving through the downstream portion of the cooling airpassage will contact the downstream battery cells for a longer period oftime (i.e., relative to the upstream battery cells). As a result, thecooling air can extract or absorb more heat from the downstreambatteries, in spite of the fact that the temperature of the downstreamcooling air is higher than the temperature of the upstream cooling air.Thus, even difficult-to-cool battery cells can be effectively cooledaccording to the present teachings, such that all battery cells withinthe battery pack will have a substantially uniform temperatureregardless of the position of the battery cell along the cooling airpassage.

In another embodiment of the present teachings, the side surfaces of thebattery cells may be covered with a material, such as a paper material.For example, the side surfaces of the battery cells may be covered withwaterproof sheets before disposing the battery cells in the battery packhousing (case). In this embodiment as well, the end faces or terminalsof the battery cells may be isolated (physically separated) from thecooling air passage in order to protect the battery cell terminals andelectrical contacts disposed there between from degradation, which wasdiscussed further above. Further, the paper material disposed around theperipheral side surfaces of the battery cells, which side surfaces maydefine one wall of the cooling air passage, also may protect the batterycells from moisture and foreign substances that may be unintentionallyintroduced into the cooling air passage. Because the peripheral sidesurfaces of the battery cells are less likely to be damaged by moistureor foreign substances than the end faces or terminal contact areas, itis not necessary to strictly or completely isolate the peripheral sidesurfaces of the battery cells from the cooling air passage in thisembodiment. Thus, in this embodiment, reliable and durable battery packscan be constructed without requiring the battery cells to be disposedwithin a dual-wall case.

In another embodiment of the present teachings, at least two cooling airpassages may be defined within the battery pack. For example, the twocooling air passages may be, e.g., substantially symmetrical relative toa central plane that is defined between the end faces or terminals ofthe battery cells. If multiple battery cells are positioned side-by-sidewith the poles of adjacent battery cells disposed in oppositeorientations, and the end faces (terminals) of these battery cells areelectrically connected to each other, the multiple battery cells will beconnected in series. Thus, by utilizing series-connected battery cells,the battery pack will be capable of generating a relatively high voltageoutput. By symmetrically positioning or defining two cooling airpassages, the temperature distribution of the battery cells can beunified in order to prevent the temperature of any one particularbattery cell from increasing sharply before the other battery cells.

These aspects, features and embodiments may be utilized singularly or incombination in order to make improved rechargeable battery packs,including but not limited to rechargeable battery packs for power toolsand other battery-powered appliances. In addition, other objects,features and advantages of the present teachings will be readilyunderstood after reading the following detailed description togetherwith the accompanying drawings and the claims. Of course, the additionalfeatures and aspects disclosed herein also may be utilized singularly orin combination with the above-described aspects and features.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exploded perspective diagram of a representative batterypack according to the present teachings.

FIG. 2 shows a top view of the exterior of the battery pack shown inFIG. 1.

FIG. 3 shows a top view of the battery pack shown in FIG. 1, in whichthe outer lid has been removed.

FIG. 4 shows a bottom view of the exterior of the battery pack shown inFIG. 1.

FIG. 5 shows a side view of the exterior of the battery pack shown inFIG. 1.

FIG. 6 shows a front view of the exterior of the battery pack shown inFIG. 1.

FIG. 7 shows a rear view of the exterior of the battery pack shown inFIG. 1.

FIG. 8 shows an internal, cross-sectional view of the representativebattery pack taken along line A-A shown in FIG. 2.

FIG. 9 shows an internal cross-sectional view of the representativebattery pack taken along line B-B shown in FIG. 2.

FIG. 10 shows an internal cross-sectional view of the representativebattery pack taken along line C-C shown in FIG. 2.

FIG. 11 shows an internal cross-sectional view of the representativebattery pack taken along line D-D shown in FIG. 2.

FIG. 12 shows an internal cross-sectional view of the representativebattery pack taken along line E-E shown in FIG. 2.

FIG. 13 shows an internal cross-sectional view of the representativebattery pack taken along line F-F shown in FIG. 2.

FIG. 14 shows an internal cross-sectional view of the representativebattery pack taken along line G-G shown in FIG. 2.

FIG. 15 shows a perspective view of a battery charger suitable forre-charging the representative battery pack.

FIG. 16 shows a side view of the representative battery pack mounted ona representative battery-operated power tool.

FIG. 17 show a cross section of a representative battery cell that maybe disposed within the representative battery pack.

FIG. 18 shows an internal, cross-sectional view of a secondrepresentative battery pack according to the present teachings.

DETAILED DESCRIPTION OF THE INVENTION

In one aspect of the present teachings, battery packs may include one ormore battery cells and each battery cell may have a first batteryterminal and a second battery terminal. A housing may enclose thebattery cell(s). A cooling air intake port and a cooling air exhaustport may be defined within the housing. At least one cooling air passagemay extend between the cooling air intake port and the cooling airexhaust port. Optionally, the at least one cooling air passage is atleast partially defined by at least one peripheral side surface of thebattery cell(s) and an inner surface of the housing, so that cooling aircan directly communicate with the at least one peripheral side surfaceof the battery cell(s).

Optionally, at least one isolated space is also defined within thehousing and the at least one isolated space is shielded from the atleast cooling air passage. Further, at least one first or second batteryterminal is disposed within the at least one isolated space. Inaddition, the housing may also include at least one securing wall thatfurther defines the at least one cooling air passage and separates theat least one cooling air passage from the at least one isolated space.Optionally, a temperature sensor, such as a thermistor, may be disposedwithin the at least one isolated space.

In another embodiment of the present teachings, a plurality of batterycells may be positioned side-by-side such that the respective firstbattery terminals are positioned within the same plane, and theterminals of the battery cells are electrically connected to each other.Further, the battery cells may have an elongated shape and the at leastone cooling air passage may extend transversely to the longitudinaldirection of the elongated battery cells.

Optionally, insulating material may be disposed at an upstream portionof the at least one cooling air passage. For example, the insulatingmaterial may comprise a relatively rigid resin cover disposed on theperipheral side surface of at least one battery cell. In addition, anair gap or air layer may be defined between the peripheral side surfaceof the at least one battery cell and the relatively rigid resin cover.In addition or in the alternative, heat sink material may be disposed ata downstream portion of the at least one cooling air passage. The heatsink material may be positioned to assist in cooling one or moredownstream battery cells.

In another optional embodiment, at least one air direction changer maybe disposed within the at least one cooling air passage. The at leastone air direction changer preferably directs cooling air flowing throughthe at least one cooling air passage toward at least one peripheral sidesurfaces of one or more downstream battery cells.

In another optional embodiment, the area of the peripheral side surfacesof upstream battery cells that directly communicates with the at leastone cooling air passage may be less than the area of the peripheral sidesurfaces of downstream battery cells that directly communicates with theat least one cooling air passage. For example, the cross-section of thecooling air passage may increase from the upstream side of the coolingair passage to the downstream side of the cooling air passage.

In another optional embodiment, waterproof material may be disposed onor may substantially surround at least one battery cell. In addition orin the alternative, moisture absorbing material may be disposed on ormay substantially surround the at least one battery cell. For example,the moisture absorbing material may be disposed between at least onebattery cell and the waterproof material.

In another optional embodiment, the at least one cooling air passage mayinclude a first cooling air passage that is substantially symmetricallypositioned relative to a second cooling air passage. Preferably, theplurality of battery cells is disposed between the first and secondcooling air passages. In another preferred embodiment, the first coolingair passage may be shorter than the second cooling air passage. Inaddition or in the alternative, the cross-section of the first coolingair passage may be different (e.g., wider or narrower) than thecross-section of the second cooling air passage.

In another embodiment of the present teachings, the battery pack housingoptionally may comprise separate top and bottom halves. A first securingwall or battery support may extend upwardly (i.e., substantiallyperpendicularly) from the bottom half of the battery pack housing andmay be arranged and constructed to contact at least some of the batterycells disposed within the battery pack housing. A second securing wallor battery support may extend downwardly (i.e., substantiallyperpendicularly) from the top half of the battery pack housing and alsomay be arranged and constructed to contact at least some of the batterycells disposed within the battery pack housing. Optionally, an elasticmaterial, or some other type of sealing material, may be interleavedbetween the battery cells and the first securing wall and/or the secondsecuring wall. Naturally, a person of skill in the art can easily designa variety of structures for defining a cooling air passage and one ormore isolated space(s) (i.e., spaces that do not communicate with thecooling air passage) within the battery pack and the person of skill inthe art is not limited to using the above-described securing walls.

Optionally, two sets of first and second securing walls may be provided.In this case, the first set of first and second securing walls maytogether define a first wall that contacts the side surfaces of thebattery cells and isolates (physically separates) a first set of endfaces (terminals) of the battery cells from the cooling air passage. Thesecond set of first and second securing walls may together define asecond wall that contacts the side surfaces of the battery cells andisolates (physically separates) a second set of end faces (terminals) ofthe battery cells from the cooling air passage. Thus, the cooling airpassage may be partially defined by the first and second walls. Acooling air intake port and a cooling air exhaust port may be defined atopposite ends of the cooling air passage.

Thus, in the assembled battery pack, the cooling air passage may bedefined by the first and second walls (i.e., the two sets of first andsecond securing walls), the side surfaces of the battery cellspositioned between the first and second walls and the interior surfacesof the top and bottom halves of the housing. A first isolated space maybe defined by the first wall (i.e., one set of first and second securingwalls), the interior surface of the housing, and the end faces orterminals of the battery cells. The first isolated space preferably doesnot directly communicate with the cooling air passage. Therefore, theend faces or terminals of the battery cells may be effectively isolatedfrom directly contacting (or directly communicating with) the coolingair passage. As a result, the end faces or terminals of the batterycells can be protected or shielded from moisture and foreign substances.A second isolated space may be defined by the second wall (i.e., theother set of first and second securing walls), the interior surface ofthe housing, and the opposite end faces or terminals of the batterycells. The second isolated space also preferably does not directlycommunicate with the cooling air passage, thereby protecting orshielding the opposite end faces or terminals of the battery cells fromdegradation.

In another embodiment of the present teachings, the plurality ofelongated battery cells may be disposed substantially in parallel and ina side-by-side relationship. For example, the side surfaces of thebattery cells optionally may closely contact each other, so that heatwill be reliably conducted or transferred between battery cells.Optionally, the respective end faces (terminals) of the battery cellsmay be positioned within substantially the same plane. Thus, the batteryterminals can be easily connected and the amount of electricallyconductive material that is necessary to electrically connect therespective battery cells can be minimized.

The first and second securing walls may include a plurality ofindentations that respectively and substantially conform to the outershape of the respective battery cells. For example, if the battery cellsare cylinder-shaped, or substantially cylindrical, the indentations arepreferably semi-circular. In this case, the securing walls will closelycontact the side surfaces of the individual battery cells. Naturally, aplurality of semi-circular indentations may be spaced along thelongitudinal direction of the first and second securing walls so as tocorrespond to the spacing of the respective battery cells. Thus, whenthe securing walls are assembled (fixedly disposed) around the batterycells, the securing walls will substantially isolate the cooling airpassage from the respective end faces (terminals) of the battery cells.

In another embodiment of the present teachings, the battery cells may bedivided into two blocks of battery cells, such as a top block and abottom block. The space defined between the top and bottom blocks(stages) of battery cells is preferably isolated or shielded from theouter environment by the battery cells themselves. The first isolatedspace, which was discussed above, optionally may communicate with thesecond isolated space via the space or clearance between the top andbottom blocks of battery cells.

In another embodiment of the present teachings, the cooling air intakeport and the cooling air exhaust port may be defined on a top surface ofthe battery pack housing. The top surface is defined when the batterypack is held in a substantially vertical orientation. Further, twocooling air passages may be defined within the battery pack. A firstcooling air passage may be defined along the inner surface of the topportion (top half) of the battery pack housing and preferably extendsfrom the cooling air intake port to the cooling air exhaust port. Asecond cooling air passage may be defined at least partially along aninner surface of the bottom portion (bottom half) of the battery packhousing. The second cooling air passage preferably extends from thecooling air intake port in a direction opposite of the first cooling airpassage. Thus, the second cooling air passage may first extenddownwardly from the cooling air intake port and along an inner surfaceof a first side surface of the battery pack housing. Thereafter, thesecond cooling air passage may extend along the inner surface of thebottom portion of the battery pack housing and finally turn to extendalong a second side surface of the battery pack housing before reachingthe cooling air exhaust port.

In another embodiment of the present teachings, the air-flow resistanceof the first cooling air passage is preferably greater than the air-flowresistance of the second cooling air passage. Further, the air volume ofthe first cooling air passage is preferably less than the air volume ofthe second cooling air passage. That is, the first and second coolingair passages are preferably designed, such that a lesser amount ofcooling air will be directed to the shorter first cooling air passageand a greater amount of cooling air will be directed to the longersecond cooling air passage. Thus, a greater volume of cooling airpreferably passes through the second cooling air passage, because thesecond cooling air passage directly contacts (communicates with) agreater number of battery cells disposed within the battery pack.

In another embodiment of the present teachings, a gap (distance) may bedefined between the two sets of securing walls and the gap may partiallydefine the first and second cooling air passages. Optionally, the gap(distance) between the two sets of securing walls is preferably narroweron the upstream side of the cooling air passage and is wider on thedownstream side.

In another embodiment of the present teachings, at least one slope orramp projects within the cooling air passage toward at least onedifficult-to-cool battery cell. The slope or ramp may define an inclinedsurface on the cooling air passage. For example, the slope or ramp maynarrow or reduce the distance between the inner surface of the batterypack housing and the side surface of one or more of the battery cells.Thus, the slope or ramp can selectively direct (guide) cooling airtoward the side surface of one or more battery cells. This optionalembodiment provides an additional technique for effectively coolingdifficult-to-cool battery cells. For example, at least one slope or rampmay be advantageously disposed within the second cooling air passage.The incline of the slope or ramp may be straight or may be concave orconvex. Thus, persons of skill in the art can readily adapt or modifythis aspect of the present teachings to a particular battery pack designwithout departing from the scope of the present teachings.

Each of the additional features and method steps disclosed above andbelow may be utilized separately or in conjunction with other featuresand method steps to provide improved battery packs and methods formaking and using the same. Detailed representative examples of thepresent teachings, which examples will be described below, utilize manyof these additional features and method steps in conjunction. However,this detailed description is merely intended to teach a person of skillin the art further details for practicing preferred aspects of thepresent teachings and is not intended to limit the scope of theinvention. Therefore, combinations of features and steps disclosed inthe following detailed description may not be necessary to practice thepresent teachings in the broadest sense, and are instead taught merelyto particularly describe representative and preferred embodiments of thepresent teachings, which will be explained below in further detail withreference to the figures. Of course, embodiments, features and stepsdescribed in this specification and in the dependent claims may becombined in ways that are not specifically enumerated in order to obtainother usual and novel embodiments of the present teachings and thepresent inventor expressly contemplates such additional combinations.

FIG. 1 shows an exploded perspective diagram of a representative batterypack 99 according to the present teachings. Battery pack 99 may include,e.g., an outer lid 10, a hook 30, a base 40, a top case (top half) 50, aset 70 of battery cells 72, and a bottom case (bottom half) 80. Fourscrews 11 optionally may join the top case 50 to the bottom case 80,although naturally other fasteners may be utilized for this purpose.

In this representative embodiment, a total of ten (10) battery cells(72-1 through 72-10) are disposed within the battery pack 99. Naturally,greater or less than ten battery cells may be utilized according to thepresent teachings with only minor modifications in order to change thevoltage and current output properties of the battery pack. Each batterycell 72 may be elongated and the longitudinal axes of the respectivebattery cells 72 may be disposed in parallel, or substantially inparallel. One set of end faces (terminals) 72 a of the battery cells 72may be positioned substantially within the same (first) plane. A secondset of end faces (terminals) 72 b of the battery cells 72 may bepositioned substantially within a same (second) plane. The second planeis preferably parallel, or substantially parallel, to the first plane.

In this representative embodiment, five battery cells 72 arerespectively positioned in a side-by-side relationship in each of a topset and a bottom set (i.e., a top block of battery cells and a bottomblock of battery cells). The peripheral side surfaces of battery cells72 preferably closely contact each other so as to enable heat conduction(transfer) between battery cells 72. In the alternative, heat-conductivematerial may be disposed between the battery cells 72 so as to allowheat to be effectively conducted or transferred between battery cells72. By enabling efficient heat conduction or transfer between batterycells 72, all battery cells 72 can be maintained at a uniformtemperature (or a substantially uniform temperature) during charging anddischarging operations. Therefore, it is further possible to prevent orsubstantially reduce the likelihood that one battery cell 72 willsignificantly overheat and become damaged.

For example, it is desirable to avoid the possibility that one batterycell 72 will reach a significantly higher temperature than the otherbattery cells 72, because the high temperature could permanently damagethe overheated battery cell 72. High temperature (i.e., overheating) maycause internal damage to battery cell 72, which may be a nickel metalhydride cell, or may cause disconnection or separation of electricalcontacts 73 between battery cells 72. Thus, by enabling efficient heatconduction or transfer between battery cells 72, the possibility of suchan undesirable high temperature condition can be minimized oreliminated. Of course, a variety of techniques may be utilized, inaddition to the present techniques or in the alternative to the presentteachings, in order to ensure adequate heat conduction between batterycells 72. The present teachings are not particularly limited in thisregard.

As shown in FIG. 17, each battery cell 72 optionally may comprisebattery core 76 surrounded, or substantially surrounded, by one or morelayers 77, 78, 79 of paper material(s). Outer layer 79 may preferablycomprise waterproof paper material. Intermediate layer 78 may preferablybe electrically insulating paper material. However, intermediate layer78 is preferably capable of conducting heat. Further, inner layer 77preferably may comprise moisture absorbing paper material. In this case,inner layer 77 can absorb any electrolyte that might leak from batterycore 76. If inner layer 77 absorbs moisture (e.g., electrolyte) andouter layer 79 is waterproof, electrolyte can be prevented from seepingor leaking into the cooling air passage and thus to outside of thebattery pack 99. In addition, layers 77, 78, 79 preferably electricallyinsulate battery core 76, but enable heat conduction from battery core76.

Electrical contacts 73 may be metal plates (e.g., lead) or another typeof electrodes. As noted above, electrical contacts 73 may be utilized toelectrically connect the end faces (terminals) 72 a and 72 b of batterycells 72 in order to provide the appropriate battery output voltage andoutput current for the desired application of battery pack 99.Naturally, a variety of arrangements for electrical contacts 73 may beutilized depending upon the desired battery voltage and output currentthat will be supplied by battery pack 99. The present teachings are notparticularly limited in this regard.

The battery cells 72 may be positioned such that their poles (i.e.,positive and negative terminals) are oriented in opposite directions foradjacent battery cells 72. For example, if the left side of battery cell72-1 is a positive terminal, the left side of the adjacent battery cell72-2 is preferably a negative terminal. As noted above, the end faces 72a of adjacent battery cells 72 may be electrically connected to eachother by electrical contacts 73 that comprise lead plates. Similarly,end faces 72 b also may be electrically connected by a separate set ofelectrical contacts 73 that comprise lead plates. For example, all tenbattery cells 72 may be series-connected using a set of lead plates 73.The respective lead plates 73 may be welded to the respective end faces72 a and 72 b of battery cells 72, thereby providing both electricalconnection and a durable physical connection or attachment betweenbattery cells 72.

As noted above, the representative battery pack 99 contains five batterycells 72 that are positioned side-by-side in the horizontal directionand their side surfaces closely contact each other, thereby defining afirst block (set) of battery cells 72. Another five battery cells 72 arepositioned in the same manner in order to define a second block (set) ofbattery cells 72. The first and second blocks (sets) may be disposed(e.g., stacked) in two stages, e.g., one block of five battery cells ontop of the other block. The peripheral side surfaces of battery cells 72preferably closely contact each other in the vertical direction as well.If paper material is disposed around battery cells 72, then theperipheral side surfaces of the paper material for each battery cell 72preferably contact each other closely (e.g., with little or no space orclearance there between).

A first insulation sheet 74 preferably covers the exterior of the leadplates 73, which lead plates 73 are respectively connected toappropriate end faces (terminals) 72 a of battery cells 72. Similarly, asecond insulation sheet 71 preferably covers the exterior of the leadplates 73 that are connected to the end faces (terminals) 72 b.

The battery cells 72 may be disposed within bottom case (half) 80 andbottom case 80 may be defined as a box having bottom plate 90 and sideplates 82, both of which are integrally formed from a resin. The topportion of bottom case 80 may be substantially open. Bottom case 80 alsomay include one or more screw hole(s) 81. Outer lid 10 may be secured tobottom case 80 using one or more screw(s) 11 that threadably engage thescrew hole(s) 81.

First and second securing walls 86 and 87 may extend perpendicularly, orsubstantially perpendicularly, to the longitudinal (elongated) directionof the battery cells 72 and may project from the inner surface of bottomplate 90. A plurality of semi-circular (concave) recesses 86 a and 87 amay be defined within the upper surfaces of the first and secondsecuring walls 86, 87. The semi-circular recesses 86 a and 87 a arepreferably designed to closely receive and contact the peripheral sidesurfaces of battery cells 72. For example, five semi-circular recesses86 a and 87 a may be disposed in series along each of the first andsecond securing walls 86 and 87. When the battery cells 72 are placedwithin bottom case 80, the bottom halves (i.e., downward facingsurfaces) of the peripheral side surfaces of the five battery cells 72on the bottom side of battery cells 72 fit into the semi-circularrecesses 86 a and 87 a, thereby securing battery cells 72 within bottomcase 80. In this state, the side surfaces of adjacent battery cells 72tightly contact each other.

First and second securing walls 86 and 87 serve to position the sidesurfaces of the five battery cells 72 above the inner surface of bottomplate 90. Consequently, a space or gap is defined between the sidesurfaces of battery cells 72 on the inner surface of bottom plate 90. Aswill be further described below, second cooling air passage 92 may bedefined by the space or clearance between the side surfaces of batterycells 72 and the inner surface of bottom plate 90, which is furtherdefined by first and second securing walls 86 and 87. That is, secondcooling air passage 92 may be surrounded and defined by first and secondsecuring walls 86 and 87, the peripheral side surfaces of battery cells72, and bottom case 80.

If semi-circular recesses 86 a and 87 a are defined on the uppersurfaces of first and second securing walls 86 and 87, the uppersurfaces of securing walls 86 and 87 will closely contact the sidesurfaces of battery cells 72 without any gaps or clearances therebetween. In this case, second cooling air passage 92, which is partiallydefined by first and second securing walls 86 and 87, will be isolatedin an airtight manner (or substantially airtight manner) from the spacesdefined on the opposite sides of first and second securing walls 86 and87. Thus, first isolated space 93 may be defined between first securingwall 86 and side wall 82 c of the bottom case 80 and second isolatedspace 95 may be defined between second securing wall 87 and side wall 82a of bottom case 80. As discussed further below, first isolated space 93may communicate with second isolated space 93. Preferably, neither offirst isolated space 93 or second isolated space 95 communicates withthe cooling air passages 91, 92.

As shown in FIGS. 10-14, first securing wall 86 preferably contacts theperipheral side surfaces of battery cells 72 near the right-side endface (terminal) 72 a, thereby isolating the right-side end face 72 a ofbattery cells 72 from second cooling air passage 92. Similarly, secondsecuring wall 87 preferably contacts the peripheral side surfaces ofbattery cells 72 near the left-side end face (terminal) 72 b, therebyisolating the left-side end face 72 b of battery cells 72 from secondcooling air passage 92. Thus, first and second securing walls 86 and 87may serve to isolate the end faces (terminals) 72 a and 72 b fromdirectly communicating with the cooling air that passes (e.g., forciblyblown) through second cooling air passage 92. As a result, first andsecond securing walls 86 and 87 prevent, or at least significantlyreduce, the possibility that the end faces 72 a and 72 b (or theelectrical contacts 73 there between) will degrade due to contact withmoisture or foreign substances introduced when cooling air is forciblymoved through second cooling air passage 92.

Thus, electrical contacts (lead plates) 73 and end faces (terminals) 72a and 72 b of battery cells 72 are not electrically insulated and aredisposed within the first and second isolated spaces that are defined onthe outside-facing surfaces of first and second securing walls 86 and87. Therefore, any moisture and foreign substances that may enter intothe interior of battery pack 99 together with the cooling air will beprevented from reaching end faces (terminals) 72 a and 72 b of batterycells 72.

As will be further described below, the cooling air proceeds from rightto left in FIG. 1 through second cooling air passage 92 that is definedbetween first and second securing walls 86 and 87. In FIG. 1, the rightside is the upstream side of second cooling air passage 92. The distancebetween first and second securing walls 86 and 87 is preferably narroweron the upstream side and is wider on the downstream side.

For example, FIG. 14 shows a cross section of the upstream side ofsecond cooling air passage 92. As shown in FIG. 14, distance L1 isdefined between first and second securing walls 86 and 87 and distanceL1 is relatively narrow. FIG. 13 shows a cross section of second coolingair passage 92 further downstream and the width of second cooling airpassage 92 has expanded to distance L2. FIG. 12 shows a cross section ofsecond cooling air passage 92 even further downstream and the width ofsecond cooling air passage 92 has expanded to distance L3. Thus, thearea of the side surfaces of battery cells 72 that directly contacts orcommunicates with second cooling air passage 92 is smaller or less forbattery cells 72 on the upstream side of second cooling air passage 92.Consequently, the area of the side surface of battery cells 72 thatdirectly contacts or communicates with second cooling air passage 92 isgreater or larger for battery cells 72 on the downstream side of secondcooling air passage 92.

As the cooling air approaches the downstream side of second cooling airpassage 92, the temperature of the cooling air will increase, becausethe cooling air will have absorbed heat from the upstream battery cells72. Thus, the downstream battery cells will be more difficult to cool,because the temperature of the cooling air is higher or hotter. However,if a larger area of these difficult-to-cool (downstream) battery cells72 is exposed to (e.g., directly contacts or communicates with) secondcooling air passage 92, all of battery cells 72 may be uniformly cooled.Thus, by expanding the cross-section of second cooling air passage 92from the upstream side to the downstream side, the temperatures of thebattery cells 72 on the upstream side and the battery cells 72 on thedownstream side may be substantially uniform, even though the coolingair that contacts the downstream battery cells 72 has become warmer.

Referring back to FIG. 1, one or more slopes (ramps) 83, 84, and 85 maybe defined on the inner surface of bottom plate 90. Slopes 83, 84, and85 may be inclined toward respective peripheral side surfaces of batterycells 72 toward the downstream side of the cooling air. Thus, slopes 83,84 and 85 may be positioned or disposed within the downstream portion ofsecond cooling air passage 92. In addition, two slopes 83 and 84optionally may be provided for a single battery cell 72 at the furthestdownstream position.

As shown in FIG. 8, slope 85 may serve to change the direction of thecooling air flowing along the inner surface of bottom case 80. Forexample, slope 85 may cause a portion of the cooling air to directlycontact or impact the side surface of battery cell 72-6 instead offlowing in parallel, or substantially in parallel, to the side surfaceof battery cell 72-6. As shown in FIG. 9, slope 84 also may serve tochange the direction of the cooling air flowing along the inner surfaceof bottom case 80. Slope 83 may have an identical construction withslope 84 and may be disposed substantially in parallel with slope 84along the second cooling air passage 92. Slopes 83 and 84 mayrespectively cause portions of the cooling air to directly contact orimpact the side surfaces of battery cells 72-8 and 72-10. Slopes 83, 84and 85 may also be interchangeably referred to as air direction changers83, 84 and 85 or cooling air directors 83, 84, and 85.

Thus, slopes 83, 84, and 85 may be utilized to change the direction of aportion of the cooling air flowing along second cooling air passage 92.For example, slopes 83, 84 and 85 may be utilized to direct a portion ofthe cooling air directly toward one or more side surfaces of batterycells 72. By directly impacting the cooling air against a particularbattery cell, it is possible to more effectively cool that particularbattery cell. Thus, if one or more battery cells within battery pack 99is particularly difficult to effectively cool, one or more slopes (airdirection changers or cooling air directors) may be defined along thecooling air passage in order to direct more cooling air against thesurface of the difficult-to-cool battery cell. In this case, it ispossible to more effectively cool such difficult-to-cool battery cellsand ensure that all battery cells 72 within battery pack 99 will bemaintained at substantially the same temperature during a chargingoperation.

As shown in FIG. 1, walls 88 and 89 also may be optionally utilized asauxiliary walls for supporting the side surfaces of battery cells 72.Although not shown by FIG. 1, a second set of walls 88 and 89 may bedefined on the opposite-end side, which is hidden from view by side wall82 of the bottom case 80.

Further, a plurality of top surfaces 51 may be defined on the upperportion of top case (top half) 50. Each top surface 51 preferably has asemi-circular interior surface that is arranged and constructed toclosely receive and contact the top half of the side surface of the fivebattery cells 72. When outer lid 10 is secured to bottom case 80, topcase 50 will closely contact bottom case 80. Further, the top halves ofthe side surfaces of the five battery cells 72 on the top side ofbattery cells 72 will contact the semi-circular surfaces on the insideof semi-circular shaped top surfaces 51. In this state, the sidesurfaces of battery cells 72 that are adjacent to each other in thehorizontal direction will firmly contact each other. Naturally, the sidesurfaces of battery cells 72 that are adjacent to each other in thevertical direction also will firmly contact each other.

Walls 56 and 60 may be defined substantially in the center of top case50 and may each have a duct shape. A cooling air intake port 52 may bedefined approximately in the center of the top case 50 and a cooling airexhaust port 55 may be defined along the left edge of top case 50.Duct-shaped wall 56 may serve to permit cooling air intake port 52 todirectly communicate with cooling air exhaust port 55, thereby definingfirst cooling air passage 91 on the back side of duct-shaped wall 56. Asdiscussed above, second cooling air passage 92 may be defined on theback-side of duct-shaped wall 60 and may guide or direct cooling airintroduced from cooling air intake port 52 to the right side of FIG. 1.A branching plate 61 may be utilized to split or separate the coolingair into first cooling air passage 91 and second cooling air passage 92and branching plate 61 may be disposed within cooling air intake port52.

As shown in FIG. 8, first cooling air passage 91 primarily serves tocool battery cells 72-5, 72-7, and 72-9. If only three battery cells arecooled by the portion of the cooling air that is directed through firstcooling air passage 91, all three battery cells can be effectivelycooled, including battery cell 72-9 located furthest downstream.Therefore, the volume of cooling air flowing through first cooling airpassage 91 may be less than the volume of cooling air flowing throughsecond cooling air passage 92. For example, the air-flow resistance offirst cooling air passage 91 may be higher or greater than the air-flowresistance of second cooling air passage 92.

Still referring to FIG. 8, second cooling air passage 92 may be definedalong the back side of duct-shaped wall 60 and may first contact(communicate with) the right side of battery cells 72. Second coolingair passage 92 then extends to the space between first and secondsecuring walls 86 and 87. The cooling air flowing through second coolingair passage 92 cools battery cells 72-3, 72-1, 72-2, 72-4, 72-6, 72-8,and 72-10 in that sequence. As the cooling air proceeds downstream, thecooling air will become increasingly heated (higher temperature), as wasdiscussed above. Thus, the downstream cooling air will be less effectivefor cooling the battery cells than the upstream cooling air.

In known designs, the battery cell that is located furthest downstream(e.g., battery cell 72-10 in this embodiment) is typically notadequately cooled, because this downstream battery will be contacted andcooled by the warmest cooling air. However, in this representativeembodiment, the cooling air will bend around battery cell 72-10, therebycontacting and cooling a relatively larger area of battery cell 72-10.Consequently, in this representative embodiment, battery cell 72-8 ismore prone to experience large temperature increases due to inefficientcooling than battery cell 72-10.

As discussed above, several techniques may be utilized in order to moreeffectively cool such a difficult-to-cool battery cell. For example, arelatively larger area of the side surface of battery cell 72-8 may beexposed to the cooling air flowing through second cooling air passage92, e.g., by defining one or more slopes 83 and 84 in the vicinity ofbattery cell 72-8. Thus, a greater portion of the cooling air willdirectly impact battery cell 72-8, thereby cooling battery cell 72-8more effectively. In addition or in the alternative, the space definedbetween first and second securing walls 86 and 87 may be widened (i.e.,thereby widening the cross-section of second cooling air passage 92) inorder to expose more surface area of battery cell 72-8 to the coolingair. However, even in that case, battery cell 72-8 may still bedifficult to cool. Thus, by forcing a relatively large volume of coolingair through second cooling air passage 92, battery cell 72-8 may beprevented from being subjected to excessive temperature increases.

According to this design, battery cells 72-3, 72-1, and 72-2, which arelocated on the upstream side of second cooling air passage 92, may beover-cooled, relatively speaking, because the upstream cooling air willbe cooler (lower temperature) than the downstream cooling air. Inparticular, battery cell 72-1 may be cooled very effectively, becausebattery cell 72-1 is located at a corner and both the top and sidesurfaces of battery cell 72-1 face (directly contact or communicatewith) second cooling air passage 92.

Therefore, in this embodiment, in order to prevent battery cells 72-3,72-1, and 72-2 from being overcooled, an insulating material 75optionally may be disposed on the peripheral side surfaces of batterycells 72-3, 72-1 and 72-2 that face second cooling air passage 92. Thus,by making it more difficult to cool battery cells 72-3, 72-1 and 72-2(i.e., by shielding battery cells 72-3, 72-1 and 72-2 with insulatingmaterial 75), the temperature of the cooling air within second coolingair passage 92 will increase less when the cooling air passes throughthe upstream portion of second cooling air passage 92. Therefore, thecooling air contacting the downstream battery cells (e.g., battery cells72-8 and 72-10) will be cooler (lower temperature) than an embodiment inwhich no insulating material is utilized. Consequently, all the batterycells 72 may be substantially uniformly cooled so as to maintainsubstantially the same temperatures.

Thus, a single second cooling air passage 92 may extend along aplurality of battery cells 72 to thereby sequentially cool the batterycells 72. In this case, it is possible to uniformly maintain thetemperature of the plurality of battery cells 72 by covering the batterycells on the upstream side (e.g., one or more of battery cells 72-3,72-1 and 72-2) with insulating material 75, thereby making the upstreambattery cells more difficult to cool. By utilizing one or moreair-direction changers 83 and 84, and by increasing amount of thesurface area of the downstream battery cells (e.g., one or both ofbattery cells 72-8 and 72-10) that directly communicates with secondcooling air passage 92, even the downstream battery cells may beeffectively cooled.

Referring back to FIG. 1, a pair of bosses 53 may extend from the topsurface of top case 50. Base 40 may be secured to bosses 83 using one ormore screws 43. A positive terminal 41, a ground terminal 45, and athermistor terminal 42 may be disposed on the top surface of base 40.Positive terminal 41 may be connected to the last positive electrode 73a of battery cells 72, which are connected in series in this embodiment,using an electrical contact (e.g., a lead plate (not shown)). Thiselectrical contact may pass through opening 57, which is defined withintop case 50. Ground terminal 45 may be connected to the last negativeelectrode 73 b of battery cells 72 using an electrical contact (e.g., alead plate (not shown)). This electrical contact may pass throughopening 59 defined within top case 50.

Thermistor terminal 42 may be connected to thermistor TH. As shown inFIG. 8, thermistor TH may be disposed within the gap or space betweenthe first and second blocks of battery cells 72. The electrical contact(e.g., a lead plate that electrically couples thermistor terminal 42 tothermistor TH) may pass through opening 58 defined within top case 50.As long as the temperature of the plurality of battery cells 72 is at orbelow a predetermined temperature, the positive voltage of battery cells72 will be supplied to thermistor terminal 42. However, when the batterytemperature reaches or exceeds the predetermined temperature, thermistorTH will disconnect and the voltage at thermistor terminal 42 will float.By monitoring voltage changes at thermistor terminal 42, it is possibleto determine whether or not the temperature of battery cells 72 is at orbelow the predetermined temperature, i.e., whether or not the batterytemperature has increased above the predetermined temperature. Thus,thermistor TH may be utilized to determine whether a maximum allowablebattery temperature has been reached. If the battery temperature becomesexcessive, charging of the battery cells may be discontinued until thebattery temperature sufficiently decreases, thereby preventing permanentdamage to the battery cells.

As shown in FIG. 1, battery pack 99 may be connected, e.g., to batterycharger 100 (shown in FIG. 15) or power tool 110 (shown in FIG. 16) bymoving battery pack 99 in the direction of arrow A with respect tocharger 100 or power tool 110. Thus, charger 100 and power tool 110 eachpreferably each include three terminals that extend in the direction ofArrow B shown in FIG. 1. In that case, when battery pack 99 is moved inthe direction of Arrow A and is installed, the positive terminal ofcharger 100 or power tool 110 will be connected to positive terminal 41.Further, the grounding terminal of charger 100 or power tool 110 will beconnected to grounding terminal 45 and a thermistor signal detectionterminal will be connected to the thermistor terminal 42. When batterypack 99 is installed in charger 100 for recharging, a charging currentwill be supplied between positive terminal 41 and grounding terminal 45in order to recharge battery cells 72. At the same time, charger 100 maymonitor thermistor terminal 42 in order to monitor abnormal temperatureincreases within battery pack 99. When battery pack 99 is installed inpower tool 110 in order to drive power tool 110, drive current issupplied to power tool 110 across positive terminal 41 and groundingterminal 45.

A signal terminal 44 also may be secured to base 40. Signal terminal 44may include a terminal for receiving a constant voltage, a groundingterminal, a battery temperature terminal for communicating signalsrepresentative of the temperature of battery cells 72, and an IDterminal for outputting an identification signal unique to each batterypack 99. Thus, when battery pack 99 is installed in charger 100, signalterminal 44 will be connected to the signal terminal on the chargerside, thereby enabling signals to be communicated between charger 100and battery pack 99.

Thermistor TH is preferably connected to the battery temperatureterminal. In this case, the voltage at the battery temperature terminalwill change as the temperature of battery cells 72 changes. As notedabove, thermistor TH may be disposed within the gap or space (e.g., anisolated space) between battery cells 72. A memory (e.g., an EEPROM) maybe coupled to the ID terminal and the memory may store an identificationnumber or signal that is unique for each battery pack 99. The memory(EEPROM) may be secured to the rear side of base 40. Various types ofinformation, such as the specification, characteristics, andcharging/discharging history of battery pack 99, may be stored in theEEPROM. By reading the information stored in the EEPROM, charger 100 canensure selection of the proper charging mode (method) for battery pack99.

As described above, thermistor TH is preferably disposed within the gapor space between battery cells 72 that is isolated from first and secondcooling air passages 91 and 92. For example, thermistor TH may bedisposed within a gap or space that is surrounded by battery cells 72 inall four directions. If the side surfaces of battery cells 72 closelycontact each other, the gap or space between battery cells 72 will beisolated from first and second cooling air passages 91 and 92. Thus,lead plates 73, end faces (terminals) 72 a and 72 b of battery cells 72and thermistor TH will be isolated from first and second cooling airpassages 91 and 92. In particular, by isolating thermistor TH fromcooling air passages 91 and 92, more accurate battery temperaturereadings can be obtained, because thermistor TH is disposed within astagnate (isolated) air space that is surrounded and substantiallyenclosed by side portions of battery cells 72.

Hook 30 may be slidably disposed between top case 50 and outer lid 10such that hook 30 can vertically slide (i.e., slide perpendicularly tothe flat surface of the outer lid 10). Spring 32 may upwardly bias orurge hook 30. As shown in FIG. 8, upper tip 33 of hook 30 may protrudeor project upwardly (i.e., perpendicularly) from outer lid 10. Whenbattery pack 99 is connected to charger 100 or power tool 110 (e.g., bysliding battery pack 99 in the direction of arrow A), the securing wallprovided in charger 100 or power tool 100 contacts the tapered surface33 a of upper tip 33 of the hook 30. As a result, hook 30 will be pusheddown. When battery pack 99 slides in the direction of arrow A untilbattery pack 99 is completely connected to charger 100 or power tool110, the securing wall provided in charger 100 or power tool 110 movesaround to the right side of upper tip 33 of the hook. As a result,spring 32 will raise hook 30. In this state, battery pack 99 isprevented from moving in the direction of arrow B relative to charger100 or power tool 110. In other words, battery pack 99 is prevented fromdisengaging from charger 100 or power tool 110. In order to removebattery pack 99 from charger 100 or power tool 110, the operator mustmanually push down protruding portion 31 of hook 30, thereby releasingthe disengagement prevention mechanism.

As shown in FIG. 1, outer lid 10 is placed over the top side of top case50. Cooling air intake port 12 may be defined within approximately thecenter of the top surface of outer lid 10, and may communicate withcooling air intake port 52 of top case 50. Preferably, charger 100includes cooling air exhaust port 104 and cooling air is forciblyexhausted from charger 100, e.g. by a fan or blower. When battery pack99 is connected to charger 100, cooling air intake port 12 of top lid 10communicates with cooling air exhaust port 104 of charger 100. As aresult, cooling air is forcibly blown from charger 100 into cooling airintake port 12 during the battery recharging operation.

Cooling air exhaust port 14 may be defined on the left edge of the topsurface of top lid 10. As shown in FIG. 8, cooling air exhaust port 14communicates with cooling air exhaust port 55 of top case 50 and theouter surface of wall 62, which is defined on the left side of top case50. Because second cooling air passage 92 communicates with the outersurface of wall 62 on the left side of top case 50, cooling air(identified by numeral 94 in FIG. 8) that has passed through secondcooling air passage 92 is also exhausted from exhaust opening 14.

Referring back to FIG. 1, outer lid 10 may include a variety ofopenings. Slot 13 may serve to guide the positive terminal of charger100 or power tool 110 and lead it to positive terminal 41. Slot 16 mayserve to guide the grounding terminal of charger 100 or power tool 110and lead it to grounding terminal 45. Slot 19 may serve to guide thethermistor terminal of charger 100 or power tool 110 and lead it tothermistor terminal 42. Opening 15 enables the signal terminal ofcharger 100 or power tool 110 to be connected to signal terminal 44.Opening 17 enables upper tip 33 of hook 30 to protrude or project aboveupper lid 10.

In the representative assembled battery pack 99, first cooling airpassage 91 and second cooling air passage 92 are symmetric (orsubstantially symmetric) relative to the central plane defined betweenthe respective end faces (terminals) 72 a and 72 b of battery cells 72.When an equal number of battery cells 72 with positive poles (terminal)are disposed on the right and left sides of battery cells 72,temperature differences between battery cells 72 can be minimized bysymmetrically providing cooling air passages 91 and 92.

The space inside the battery pack housing, which space is defined by topcase 50 and bottom case 80, is basically divided into two types ofspaces. The first type of space is the space between first and secondsecuring walls 86 and 87, which space includes first and second coolingair passages 91 and 92. The second type of space includes the twoisolated spaces 93 and 95 that are disposed external to first and secondsecuring walls 86 and 87. First isolated space 93 is isolated andseparated from first and second cooling air passages 91 and 92, becausefirst securing wall 86 contacts the side surface near the left-bottomend face 72 a of battery cells 72. Further, the inner surface of topcase 50 contacts the side surface near the left-bottom end face 72 a ofbattery cells 72. Similarly, second isolated space 95 is isolated andseparated from first and second cooling air passages 91 and 92, becausesecond securing wall 87 contacts the side surface near the right-top endface 72 b of battery cells 72. Further, the inner surface of top case 50contacts the side surface near the right-top end face 72 b of batterycells 72.

First isolated space 93 may be connected to (communicated with) secondisolated space 95 via the space or clearance (gap) between the batterycells, which space or clearance is also preferably isolated by batterycells 72 from first and second cooling air passages 91 and 92. End faces(terminals) 72 a and 72 b, lead plates 73, and the parts comprising theelectrical circuits, such as thermistor TH, are preferably disposedwithin first and second isolated spaces 93 and 95. In that case, batterypack 99 will be highly resistant to moisture and foreign substances andwill be durable, because the components that are most sensitive todegradation will be shielded from moisture and foreign substances thatcould be introduced into the interior of battery pack 99 by the coolingair. Further, by directly cooling the side surfaces of battery cells 72(i.e., directly contacting the cooling air with the side surfaces ofbattery cells 72), overheating of battery cells 72 can be effectivelyprevented. Moreover, by utilizing one or more of the above describedcooling capability enhancement techniques, temperature differences amongthe individual battery cells 72 can be successfully restricted to arelatively small temperature range.

Battery pack 99 of a second representative embodiment is shown in FIG.18. Because second representative battery pack 99 is substantiallysimilar to first representative battery pack 99 and includes many commonelements, only a description of elements that differ from the firstrepresentative battery pack 99 will be provided. The descriptionconcerning common aspects and elements of first representative batterypack 99 are thus incorporated by reference into the description ofsecond representative battery pack 99.

Second representative battery pack 99 includes air gap or clearance 75a, which is defined between battery cells 72 and insulating material 75.In this embodiment, insulating material 75 may preferably be formed as asubstantially rigid material that will reliably define air gap 75 a. Forexample, insulating material 75 may be a polymer-based material,although a variety of materials may be utilized to form insulatingmaterial 75. Air gap 75 a thus provides an insulating air layer betweenbattery cells 72 and cooling air passages 91, 92, thereby reducing theability of cooling air passages 91, 92 to cool, e.g., battery cell 72-3,which is disposed on the upstream side of cooling air passages 91, 92.

Further, heat sink material 120 may be disposed around or contact one ormore of the difficult-to-cool battery cells 72 that are disposed on thedownstream side of cooling air passages 91, 92. For example, heat sinkmaterial 120 may be disposed on one or more of battery cells 72-6, 72-8and/or 72-10. Heat sink material 120 may comprise, e.g., a metalmaterial and preferably serves to conduct or transfer heat away frombattery cells 72 to cooling air passages 91, 92, thereby moreefficiently cooling the difficult-to-cool battery cells 72.

By providing insulating material 75 and air gap 75 a on the upstreamside of cooling air passages 91, 92 and by providing heat sink material120 on the downstream side of cooling air passages 91, 92, battery cells72 may be uniformly cooled. Further, if insulating material 75 and airgap 75 a are utilized on the upstream side, the amount of heat sinkmaterial 120 disposed on the downstream side can be minimized. However,a person of skill in the art will recognize that insulating material 75,air gap 75 a and heat sink material 120 are optional elements and none,one, two or all these elements may be utilized in any combinationaccording to the present teachings.

Battery packs 99 according to the first and second representativeembodiments possess the same level of reliability as obtained bydisposing the battery cells within a dual-wall case while at the sametime achieving an overall weight reduction of 8 to 10%. Themanufacturing cost can also be significantly reduced. Thus, battery pack99 offer several advantages as compared to the known art.

As noted above, various modifications can be made to the presentteachings without departing from the scope of the present teachings. Inaddition, various techniques may be combined with the present teachingsin order to define additional useful embodiments of the presentteachings. For example, relevant battery charging techniques and batterypack designs are also taught in commonly-assigned U.S. Pat. Nos.5,909,101, 5,912,546, 6,066,938, 6,075,347, 6,124,698, 6,191,554,6,191,560, 6,204,640, 6,204,641, 6,225,786, 6,229,280, 6,275,009,6,278,261, 6,362,600, 6,373,228, 6,404,167, 6,433,515, 6,433,517, USPatent Publication Nos. 2001-17531, 2001-48289, 2002-79867 and U.S.patent application Ser. No. 09/417,698, which corresponds to EuropeanPatent Publication No. 0 994 523, all of which are hereby incorporatedby reference in their entirety as if fully set forth herein and all ofwhich may be advantageously combined with the present teachings.

1. A battery pack, comprising: a plurality of battery cells, a housingsubstantially enclosing the plurality of battery cells, a cooling airintake port and a cooling air exhaust port defined within the housing,at least one cooling air passage extending between the cooling airintake port and the cooling air exhaust port, the at least one coolingair passage being at least partially defined by peripheral side surfacesof the battery cells, wherein the plurality of battery cells includesupstream battery cells located at an upstream portion of the at leastone cooling air passage and downstream battery cells located at adownstream portion of the at least one cooling air passage; and at leastone slope disposed within the downstream portion of the at least onecooling air passage, the at least one slope changing direction ofcooling air flowing through the at least one cooling air passage towardsthe peripheral side surface of at least one downstream battery cell. 2.A battery pack as in claim 1, wherein the at least one slope inclinestowards the peripheral side surface of at least one downstream batterycell.
 3. A battery pack as in claim 1, wherein the at least one coolingair passage is at least partially defined by the peripheral sidesurfaces of the battery cells and an inner surface of the housing, andthe at least one slope is formed on a portion of the inner surface ofthe housing that defines the downstream portion of the at least onecooling air passage.
 4. A battery pack as in claim 1, wherein the atleast one slope comprises at least two slopes that incline towards theperipheral side surface of one downstream battery cell located at thefurthest downstream position.
 5. A battery pack as in claim 1, furthercomprising an insulating member disposed at the upstream portion of theat least one cooling air passage, wherein the heat insulating member atleast partially shields the surface of at least one upstream batterycell from cooling air flowing through the at least one cooling airpassage.
 6. A battery pack as in claim 1, further comprising a heat sinkmember disposed at the downstream portion of the at least one coolingair passage, wherein the heat sink member conducts heat away from atleast one downstream battery cell.
 7. A battery pack as in claim 1,wherein the at least one cooling air passage comprises a first coolingair passage and a second cooling air passage, wherein the plurality ofthe battery cell are disposed between the first and second cooling airpassages.
 8. A battery pack as in claim 1, wherein the first cooling airpassage is shorter than the second cooling air passage and the air flowresistance of the first cooling air passage is greater than the secondcooling air passage.
 9. A battery pack as in claim 1, further comprisinga temperature sensor disposed within a gap or space within the pluralityof battery cells, which gap or space is isolated from the first andsecond cooling air passages, the temperature sensor being incommunication with at least one battery cell.
 10. A battery pack as inclaim 1, wherein the plurality of battery cells comprises elongatedbattery cells positioned side-by-side, and the at least one cooling airpassage extends transversely to the longitudinal direction of theelongated battery cells.